In order to minimize the variation in output flow of hydraulic lost-motion metering pumps from one pump to another, it is necessary to perform a calibration procedure on each pump. The parameter that a user is most concerned with is the amount of fluid that is pumped over a given time. This parameter, in turn, is determined by the physical relationship between a bypass hole located in a hollow plunger and a control rod extending into the hollow plunger. Currently, this relationship is adjusted during a calibration procedure, which is conducted before filling of a pump reservoir, by an air gauging setup. Briefly, the air gauging setup measures the pressure drop across the bypass hole when the hollow plunger is disposed at a certain position. If a standardized pressure drop value is used for all pumps of a given configuration, then one can be assured that flow performance variations will be minimized. This pressure drop is related to the amount of air flowing through the bypass hole, which is, in turn, related to the equivalent size of the bypass hole when the plunger is at the certain position. The size of the bypass at the time that the plunger is disposed at the certain position can be adjusted by changing the position of the control rod relative to the bypass hole. Typically, a stamped metal linkage is bent to accomplish the actual adjustment of control rod position.
Bending the metal linkage to obtain the desired pressure drop value is a lengthy and tedious process. In addition, calibration must be performed very early in the assembly process. If it ever becomes necessary to re-calibrate the pump, substantial disassembly of the pump is required. Furthermore, if re-calibration of the pump is required once the pump is installed, either the pump will have to be returned to the manufacturer or an air gauge setup will have to be provided at the installation site.